A currently foreseen development of communication in cellular networks involves numerous small autonomous devices, which transmit and receive only small amounts of data (or are polled for data) occasionally, e.g. once a week or once per minute. These devices may be sensors or actuators of different kinds, which communicate with application servers within or outside a cellular network. The application servers configure the devices and receive data from them. Hence, this type of communication is often referred to as machine-to-machine (M2M) communication and the devices may be denoted machine devices (MDs). In the 3GPP standardization such communication and devices are denoted Machine Type Communication (MTC) and Machine Type Communication devices (MTC devices), respectively. In the following, such autonomous device is denoted machine device (MD).
In view of the nature of MDs and their assumed typical uses it follows that they will often have to be very energy efficient, as external power supplies will typically not be available and since it is neither practically nor economically feasible to frequently replace or recharge their batteries. In some scenarios the MDs may not even be battery powered, relying instead on energy harvesting, i.e. gathering energy from the environment, opportunistically utilizing (the often very limited) energy that may be tapped from sun light, temperature gradients, vibrations, etc.
So far focus has been directed to MDs being directly connected to the cellular network via the radio interface of the cellular network. However, a scenario which is likely to be more prevalent is that MDs connect to the cellular network via a gateway. In such scenarios the gateway acts like a UE towards the cellular network while maintaining a local network, typically based on a short range radio technology towards the MDs. Such a local network, which in a sense extends the reach of the cellular network (to other radio technologies but not necessarily in terms of radio coverage), has been coined capillary network and the gateway connecting the capillary network to the cellular network is herein referred to as a capillary network gateway (CGW). FIG. 1 illustrates such capillary network 1, comprising a number of machine devices 21, 22, 23 communicating with the CGW 4 over a first air interface 3 typically implementing a short range radio technology. The CGW 4 is in turn communicating with a node of the cellular network 5 over a second air interface 6. An application server 8 is also illustrated.